0740 800 028
Valid from machine no. 701--xxx--xxx9208--1
LHF 630/800
Service manual
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LIST OF CONTENTS Page
RATING PLATE 3..................................................................
DESCRIPTION OF OPERATION OF LHF 630/800 4...................................
BLOCK DIAGRAM, LHF 630/800 7...................................................
COMPONENT DESCRIPTION, CIRCUIT DIAGRAM 8..................................
CIRCUIT DIAGRAM, LHF 630/800 9.................................................
DESCRIPTION OF OPERATION, CIRCUIT BOARD K70 11..............................
CIRCUIT DIAGRAM, CIRCUIT BOARD K70 14.........................................
COMPONENT POSITIONS, CIRCUIT BOARD K70 16..................................
REPLACEMENT OF THYRISTORS 18................................................
Note that only the English part of the instruction manual has been included.
INSTRUCTION MANUAL 19.........................................................
PRESENTATION 20.................................................................
INSTALLATION 22..................................................................
TECHNICAL DESCRIPTION 23......................................................
TECHNICAL DATA 23...............................................................
MAINTENANCE 24.................................................................
STATIC CHARACTERISTICS 25......................................................
EFFICIENCY
ç AND POWER FACTOR ë 25...........................................
SPARE PARTS LIST 27..............................................................
This service manual is valid from machine no 701--XXX--XXX.
The date on the front page is followed by a one (9208 --1), this means that the layout has been
altered, the contents are still the same as in 9208 though.
Rights reserved to alter specifications without notice.
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RATING PLATE
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1. The symbols indicate that the LHF 630 incorporates a transformer and a rectifier.
2. Current/voltage characteristic for MMA welding.
3. Indicates that the unit is intended for connection to a 3--phase supply at 50 or 60 Hz.
4. The machine’s serial number, consisting of three groups of figures (xxx yyy vzzz).
The first group (xxx) indicates the version. The numerals indicate the year and week of
approval of the design version.
The second group (yyy) indicates the year and week of the machine’s final testing:
e.g. 203 indicates 1992, week 3.
The final (vzzz) group consists of three or four numerals and is a consecutive serial
number from 0001 to 9999.
5. These letter and numeral combinations indicate that ESAB complies with existing nation-
al and international standards.
6. X = Intermittance factor: indicates for how long welding can be carried out at the
specified welding data, expressed as a percentage of a 5--minute period.
I
2
= Current at the respective intermittance factor.
U
2
= Arc voltage.
U
o
= No--load (open--circuit) voltage.
7. Supply voltages and primary current at various intermittance factors.
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DESCRIPTION OF OPERATION OF LHF 630/800
GENERAL DESCRIPTION
The LHF 630/800 are thyristor--controlled welding power sources incorporating mains
voltage compensation and intended for MMA welding, TIG welding and air--arc gouging.
The mains voltage compensation ensures that the arc voltage and welding current remain
stable even though supply voltage may vary. Electronic control ensures that the welding
current maintains its set value at all times. A single knob regulates the welding current over
its entire range.
The following description refers to the block diagram on page 7.
1 Reference potentiometer K57 for adjusting the welding current. The current setting
is as defined by the ISO line.
2 Reference potentiometer, connected to remote control socket K24, for remote
adjustment of the welding current.
3,4,5 Galvanically isolated remote control device.
The remote control circuit employs a double--winding transformer (K52),
associated rectifier and voltage stabilisation circuit, A/D converter, optocoupler
and D/A converter.
A pulsed voltage transfers the reference voltage from the remote control t erminal
socket via the optocoupler to the D/A converter, the output of which i s an analog
reference voltage.
6 Selector switch K33 selects local or remote control of the reference voltage.
The actual switching of the voltage reference signals is effected by analog
switches: the block diagram shows the switching only schematically.
7 Current reference boost in response to short circuits.
8 Reference voltage input from the local and external potentiometers respectively.
9 This circuit boosts the welding current in the event of an arc short circuit, thus
preventing the electrode f rom burning on to the work during welding. The current
reference signal is increased electronically via 7) and 20).
10 Assists striking of the arc by means of an elevated current reference signal during
starting. See 14), ’Hot start’.
11 Reduces the welding current in the event of a long--duration short circuit, i.e. if the
electrode has burnt on to the workpiece. See 13), ’Foldback’.
12 Input for current signal from elevated shunt voltage.
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13 Foldback.
This is a timer circuit that starts when the arc is short --circuited. It reduces the
welding current via 11) if the short circuit persists, i.e. if the electrode has burnt on
to the workpiece. This helps to protect the thyristors against abnormally high
and/or long--duration short circuits.
The foldback feature operates only in the MMA welding mode.
14 Elevated starting current (starting boost, hot start)
The starting current circuit briefly increases the welding current when starting to
weld. The peak value of the starting pulse is about twice the set value of welding
current, and gives the power source good starting characteristics during MMA
welding.
Switch K79 (see 22), below) disconnects the feature during TIG welding.
15 Power supply unit for the electronic equipment, supplying stabilised DC at ±15 V.
The neutral of the electronic circuitry is connected to the positive of the welding
voltage (+ on K13).
The power supply unit receives a three--phase alternating voltage from the
synchronising windings K1s3.
16 Control comparator/amplifier, which compares the voltage signals from 8--12) and
then amplifies the summing voltage to provide a suitable control voltage signal to
the trigger unit 17). The good dynamic welding performance of the L HF 630/800
is partly due to the characteristics of the amplifier.
The no--load detector 21) reduces the amplifier output signal when there is no arc.
17 Trigger unit
The trigger unit consists of three identical circuits (one for each phase). Each
circuit provides trigger pulses for its thyristors, with phase angles in proportion to
the output voltage from the control amplifier. Auxiliary windings on the m ain
transformer provide synchronising signals.
18 Thermal overload cutout, which interrupts the pulses to the thyristors in the event
of high temperature of t he thyristor cooling fins.
19 Shunt amplifier, amplifying the signal from the current shunt to a suitable level for
input to 12).
20 Short--circuit detector, sensing short circuits of the arc. See also 13).
21 No--load detector, senses no--load (open--circuit) voltage. See also 14) and 16).
22 Switch K79 (MMA/TIG), switching the control characteristics between MMA and
TIG. When the switch is in the TIG position, the elevated starting current and
foldback circuits are disconnected: if this were not done, there would be
considerable risk of burning through the workpiece.
Switching is effected electronically: the block d iagram shows only a schematic
representation.
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23 Control amplifier for air--arc gouging, producing a DC voltage that is proportional
to the reference voltage signal from 6), to give a constant--voltage characteristic.
The shunt signal from 19) is used to provide a current limit that protects various
parts of the system, including the thyristor rectifier 26).
24 Changeover switch for air--arc gouging, in the form of a three--position switch on
the front panel, which also controls selection of MMA and T IG welding.
(See 22).)
25 Main transformer (three--phase).
26 Thyristor r ectifier.
27 Basic current resistor, 8.6 τ ±5%.
28 Basic current rectifier.
29 Freewheel diode.
30 Shunt for measurement of welding current.
31 Inductor for smoothing welding cur rent.
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BLOCK DIAGRAM, LHF 630/800
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COMPONENT DESCRIPTION, CIRCUIT DIAGRAM
K1 Main transformer
K2.1 Main thyristors
K2.2 Main diodes
K2.3 Basic current diodes
K2.4 Freewheel diode
K6 Mains switch
K11 Mains terminal block
K12 Inductor
K13 Welding current terminals
K14 Basic current resistor, 8.6 τ ±5%.
K18 Shunt -- 120 mV at 630 A (LHF 630) and at 800 A (LHF 800).
K24 Remote control socket
K27.1 Transient protection
K27.3 Capacitor 0.1←F
K27.4 Capacitor 5←F
K28 Fan
K31 Thermal overload cutout: breaks at 68˚C, resets at 59˚C, tolerance ±3˚C.
K33 LOCAL/REMOTE control selector switch
K38 Indicating lamp, 28 V.
K45.1 Contact, 15--way, male
K45.2 Contact, 15--way, female
K45.3 Contact, 12--way, male
K45.4 Contact, 12--way, female
K45.5 Contact, 6--way, male
K45.6 Terminal block
K47 Starting capacitor for cooling fan, 3←F 400 V.
K50 Terminal block
K52 Control power supply tr ansformer, supplied at 35 V from K1s3. The secondary
winding supplies 19 V AC to circuit board K70.
K57 Potentiometer (2 kτ) f or controlling the welding current. Fine--resolution type,
fitted with planetary reduction gear.
K70 Main control circuit board
K79 Selector switch, TIG/MMA/Air-- arc gouging.
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CIRCUIT DIAGRAM, LHF 630/800
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DESCRIPTION OF OPERATION, CIRCUIT BOARD K70
This description refers to the circuit diagram on page 14. The same reference numbers that
were used in the block diagram on page 7 are also used in the description of the circuit
board.
1 Reference input.
Reference potentiometer K57 (2kτ ±10% 2W, linear) is supplied at +15V and
connected to A2, A4 and A5.
The reference voltage is limited to 0--10V by potential divider R3/R4, and connected
to analog switch IC1.
2 Remote control device.
The remote control device, which can be a potentiometer or a pulse generator, is
connected to circuit board terminals A10, A11 and A12 via remote control input K24.
It is supplied at 15 V via pins F and H in input K24. The reference voltage from the
remote control device is connected to pin G.
0 V between G and H results in minimum current, and 15 V gives maximum current.
3 A/D converter.
The A/D converter and the voltage reference unit (see 4), below) are galvanically
isolated from the rest of the control circuitry by optocoupler IC12 (see 5), below).
The A/D converter converts the reference signal to a pulse train, in which the
mark/space ratio represents the magnitude of the reference signal.
Optocoupler IC12 transfers the pulse train to t he D/A converter, thus ensuring
complete galvanic isolation between the voltage signal from the remote control input
and the other electronic equipment.
If selector switch K33 is in the REMOTE position, but no remote control device is
connected, the power source will give low welding current, as R112, in the A/D
converter 3), produces a low value of current reference signal.
4 Galvanically isolated voltage reference.
The secondary output voltage from winding K1s3 on the main transformer supplies 35
V to control power supply transformer K52. The secondary voltage from K52
supplies 19 V to remote control output voltage regulator VR1 via terminals B6 and B7
and diode bridge BR1.
The output voltage from VR1 is 16.2 V, which is reduced to 15.6 V after diode D12.
The regulator is cur rent--limited to 120 mA by resistors R104--107, transistor Q19 and
diode D12, making the remote control connection short circuit--proof.
5 The D/A converter, which recreates the mean value of the reference signal from the
pulse train from 3). The input signal is fir st amplified and filtered: trimming
potentiometer R87 adjusts the output signal from IC4:1 to 0 V when the remote
control potentiometer is at its minimum position and to +11.5 V when the
potentiometer is at its maximum position. The signal is then passed t o analog switch
IC1, which is controlled by the LOCAL/REMOTE selector switch.
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6 LOCAL/REMOTE selector switch.
Three analog switches (IC1) control signal switching for selection of local (internal)
or remote (external) control of the welding current.
These switches are, in turn, controlled by selector switch K33. The control voltage,
which can be measured at terminal A3, is either 0 V ((K33 closed = internal
reference) or about +27 V (K33 open = remote reference).
IC1 contains four identical analog switches, of which three are used for local/remote
changeover switching. The fourth switch is used for selection of the Hot Start
function. The switches conduct with a control voltage of +15 V on pins 6, 12 and 13,
and are open--circuit with a control voltage of 0 V.
15 Control power supply.
The control power supply is obtained from winding K1s3 on the main transformer,
which is connected in star. The voltage between the star point and the respective
phase terminals is about 19 V, and the star point is connected to B5, which is the
neutral in the electronic circuitry.
The phase voltages are connected to B10, B11 and B12: capacitors C51, C52 and C53
decouple any HF interference.
Resistors R125--127 are film resistors that protect the synchronising winding against
any short circuits on the circuit board. Together with capacitors C54-- C58, they also
filter out transient peaks in the 19 V supply caused by the thyristors firing.
Voltage regulator VR2 produces a +15 V stabilised voltage: trimming potentiometer
R129 pr ovides fine adjustment. Resistors R128 and R130 restrict the range over
which the voltage can be adjusted to a maximum voltage of +18 V, which is the
maximum permissible supply voltage for the CMOS circuits.
D21 stabilises the negative voltage to --15 V. The power rating of R131 is such as to
allow the circuit to supply a load current of 30 mA.
17 The trigger unit converts t he DC signal from the control amplifier 16) to ignition
pulses that fire the thyristors at the correct point in the cycle.
The unit consists of three identical sections, one for each thyristor. A synchronising
winding K1s2, connected to terminals B13--15, provides synchronising information
for correct firing. The voltage between B13/B14/B15 is approximately 35 V.
The ignition pulses are connected to each thyristor. The gate connections are twisted
together with the associated neutral connections in order to minimise the risk of
interference in the gate circuit.
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18 The thermal overload switch interrupts the power supply to output transistors Q9, Q12
and Q15 in the trigger unit in the event of excessive thyristor temperature. The switch
interrupts the circuit at a temperature of 68 ˚C, and resets automatically when the
temperature has fallen to 59˚C.
Operation of the thermal overload switch prevents the thyristors from receiving any
trigger pulses. The current flowing in the main welding circuit is then limited to the
basic current of 8 A.
19 The shunt amplifier amplifies the voltage signal from the shunt. Trimming
potentiometer R132 adjusts the output voltage from the amplifier to --20 mV when no
welding current is flowing.
The shunt provides an output voltage signal of 120 mV for 630 A welding current in
LHF 630 and 120 mV for 800 A welding current in LHF 800.
22 The MMA/TIG selector switch.
Changeover between MMA and TIG welding modes is controlled by transistor Q16,
which is controlled by switch K79.
In the MMA welding mode, the control voltage at A1 is about --25 V (switch K79
open), while in the TIG welding mode it is 0 V (K79 closed).
24 Air--arc gouging/MMA changeover.
A contact on switch K79 links contacts A9-- A12 in the galvanically isolated remote
control circuit to change the operating mode to air--arc gouging. (Switch K79 also
selects MMA or TIG welding modes.)
Optocoupler IC11 is activated in the air--arc gouging mode, and in turn activates the
air--arc gouging control circuits.
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CIRCUIT DIAGRAM, CIRCUIT BOARD K70
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COMPONENT P OSITIONS, CIRCUIT BOARD K70
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REPLACEMENT OF THYRISTORS
When fitting replacement thyristors, it is extremely important that they are correctly secured,
i.e. with a clamping force of 4500 N (450 kp) ±10% for LHF 630 and 5490--5530 N for
LHF 800.
Clean the flat surfaces of the thyristors and heat sinks carefully, and remove any burrs or
traces of grease or oil. Apply a very thin film of silicone grease to the contact surfaces of the
heat sink, and position the thyristor between the surfaces with the symbol on the thyristor
facing in the direction as shown in the diagram below. Centre the thyristor by locating the
pin projecting from the pressure cap in the depression in the thyristor body.
Start by finger--tightening the nuts enough to remove play between the nuts and washers.
Then, using a dial gauge or depth gauge, measure the distance from the plate to the spring as
shown in the diagram below.
Tighten the nuts alternately with a spanner until the distance has decreased by 0.9 ±0.05 mm
for LHF 630 and 1.0 ±0.05 mm for LHF 800.
FITTING OF THYRISTORS
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INSTRUCTION MANUAL
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WARNING
READ AND UNDERSTAND THE INSTRUCTION MANUAL BEFORE INSTALLING OR OPERATING.
ARC WELDING AND CUTTING CAN BE INJURIOUS TO YOURSELF AND OTHERS. TAKE P RECAU-
TIONS WHEN WELDING. ASK FOR YOUR EMPLOYER’S SAFETY PRACTICES WHICH SHOULD BE
BASED ON MANUFACTURERS’ HAZARD DATA.
ELECTRIC SHOCK -- Can kill
S Install and earth the welding unit in accordance with applicable standards.
S Do not touch live electrical parts or electrodes with bare skin, wet gloves or wet clothing.
S Insulate yourself from earth and the workpiece.
S Ensure your working stance is safe.
FUMES AND GASES -- Can be dangerous to health
S Keep your head out of the fumes.
S Use ventilation, extraction at the arc, or both, to keep fumes and gases from your breathing zone and the general area.
ARC RAYS -- Can injure eyes and burn skin.
S Protect your eyes and body. Use the correct welding screen and filter lens and wear protective clothing.
S Protect bystanders with suitable screens or curtains.
FIRE HAZARD
S Sparks (spatter) can cause fire. Make sure therefore that there are no inflammable materials nearby.
MALFUNCTION -- Call for expert assistance in the event of malfunction.
PROTECT YOURSELF AND OTHERS!
LHF 630 and LHF 800 -- two thyristor controlled welding rectifiers with mains voltage
compensation designed for hand welding, TIG welding and ar c--air gouging. The mains voltage
compensation ensures constant welding current and arc voltage regardless of mains voltage
variations. The electronic control circuitry maintains pre--set welding current value. A single
setting knob takes care of the entire welding current range. All LHF rectifier s are provided with
two sturdy lifting eyelets facilitating transport by crane, shop traveller or lifttruck.
Hand welding
LHF 630 and 800 have excellent striking and welding properties. The open circuit voltage and
a well balanced current boost, i.e. a start surge, facilitate striking and restriking of the electrode.
The LHF ”anti--stick” action greatly reduces the risk of the electrode sticking to the workpiece,
the welding current is quickly reduced to 8A (the basic current level), which makes it easy to
separate the electrode from the workpiece. This function primary facilitates the welding of root
runs and saves electrodes. The dynamic characteristics of the LHF produce a quiet and
spatter--free arc and an easily controlled molten pool. LHF accepts all hand welding electrodes,
including basic electrodes.
TIG welding
LHF 630 and LHF 800 are designed with optimal TIG welding characteristics. When TIG
welding thin plate, low min. current is required. LHF’s min. current of only 8A definitely
meets this demand. When TIG welding, the ”start surge” and the ”antistick” action is
disconnected by the switch located on the front panel. Suitable, optimal accessory TIG
equipment includes: auxiliary transformer, SEIRION DC or TIG-- Aid, gas bottle, gas regulator,
TIG--torch, etc.
Arc-air gouging
The LHF 630/800 have been optimized for hand welding and arc--air gouging. Arc--air gouging
is not only a way of removing welding defects, it can also be used for the preparation of root
runs and for other forms of weld preparation. It is also an efficient and prof itable method of
cleaning up and removing faults from castings as well as cutting off steel reinforcements in
concrete castings. The LHF can be used with carbon rods with diameters of up to 10 and 13 mm,
respectively. Compressed air and a torch are needed together with the LHF when arc--air gouging.
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